Solid state light emitter sources, such as light emitting diodes (LEDs) or LED chips, are widely used in lighting products for commercial and personal use, including, for example, backlighting displays for monitors and televisions. LED chips can be used in the design of compact, thin, energy-saving products having longer lifetimes than conventional lighting products on the market. Products using LED chips require less power to meet the brightness specifications for a given lighting application, thereby significantly reducing energy consumption and the need for active cooling systems. A current trend in packaging LED chips is the use of thinner molded packages for fitting into thin, possibly flat, panel display systems. Thinner packages can, for example, have increased cavity angles to assist in exceeding or maintaining brightness specifications. As cavity angles increase, package material can incompletely mold about package components. For example, package material can incompletely mold about portions of a leadframe. This can lead to gaps, voids, incomplete resin filling, and low adhesion between components within a given package.
Referring to FIGS. 1A and 1B, a prior art LED package having incomplete resin filling is illustrated. FIG. 1A schematically illustrates a cross-sectional view of an LED package, generally designated 10. FIG. 1B is an exploded view of a cavity edge portion of FIG. 1A. LED package 10 can comprise a thin, high-brightness LED package used, for example, in a thin lighting device or panel display system. As packages become thinner, a cavity angle can increase to maintain or exceed brightness levels in part by increasing surfaces from which light can be reflected. LED package 10 can comprise a body 12 molded about one or more electrical elements, for example, first and second electrical leads 14 and 16, respectively. At least one LED or LED chip, generally designated 18 can be disposed over a thermal element 20 of the package 10 and electrically communicate to the electrical elements using one or more wirebonds 22. A cavity can be formed in the body, and the cavity can comprise a cavity floor 24 and at least one cavity wall 26 extending around the cavity floor 24 such that the cavity surrounds the at least one LED 18. Cavity angle θ measures the angle between opposing sides of the cavity wall 26, the opposing sides can extend around the cavity floor and at least one LED chip 18. First and second electrical leads 14 and 16 can be disposed along a same plane as cavity floor 24, that is, electrical leads and cavity floor 24 can be flush and/or flat.
As best illustrated by the exploded view in FIG. 1B, cavity wall 26 and electrical element meet at a point P. During molding of body 12, a viscous plastic resin can be restricted from flowing into such a tight space formed at and/or adjacent point P and can incompletely fill an area adjacent point P as indicated by the solid area, generally designated 28. That is, area 28 can comprise an area of “plastic non-filling” such as a void or gap where resin cannot and/or does not flow into, and which can run at least partially along a length of the cavity wall adjacent electrical lead 14. This is undesirable as it decreases adhesion between the plastic body 12 and electrical lead 14. Electrical lead 14 may be inadequately secured within body 12 and can lead to various types of failures during operation of package 10. For example, if the electrical lead 14 shifts or moves within the package it can cause one or more wirebonds 22 to break. In addition, encapsulant or other optical material could leak out from the cavity and into the voided areas, which could interfere with light emission of the package body. Further defects can include cosmetic issues, for example, producing pattern recognition errors during production, for example during LED chip die bonding and/or wire bonding. Such leakage can also affect color point stability. Also, the inconsistent surface can make automated process steps such as die attach difficult due to pattern recognition errors.
FIG. 2 illustrates a prior art solution for resolving the problem of plastic non-filling. FIG. 2 illustrates an LED package 30 having similar features as described in FIGS. 1A and 1B, but removing a portion of the body such that a ledge, or step 32 is formed at the base of cavity wall 26. That is, cavity wall 26 does not extend in a continuous line to meet first and second electrical leads 14 and 16 at point P. Rather, cavity wall 26 extends along a continuous line until it is positioned over the electrical leads and then it descends in a substantially vertical line vertically stepping down to fit against electrical leads 14 and 16. This can decrease the amount of plastic non-filling by eliminating the tight, triangular area 28 of non-filling illustrated in FIGS. 1A and 1B. However, the brightness of LED package 30 is decreased because of step 32. A portion of the reflective surface has been removed, thus, package brightness can decrease due to the very small cup angle around the base of the cavity wall 26. Valuable reflective surfaces are is lost because of the vertical drop, and removal of at least a portion of the body.
Thus, despite the availability of various LED packages in the marketplace, a need remains for LED packages, systems and methods with improved resin filling and high adhesion while maintaining a high-brightness.